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Create an energy-saving thermal envelope for
your home

R-values | Free Copy | Art Files

Insulation slows down the heat flow through a building's envelope. A home's building envelope contains the walls, attic, roof and basement-basically everything that surrounds the space you want to keep warm in the winter and cool in the summer.

Insulation works all year long to make your home more comfortable and energy efficient. In the winter, it slows heat loss and helps prevent condensation buildup. During summer months, insulation reduces heat gain and helps keep your home cool.

Adding insulation to your home can cut heating and cooling costs anywhere from 15 to 45 percent, depending on factors such as the original amount of insulation in your home, house size, air leaks and personal energy use and living habits. Many variables affect the amount you'll save, but the fact remains that insulating your home is a wise energy investment.

While every house is different, the basic rule of insulating is the same for all homes: Install insulation on any surface separating a heated space from an unheated space. Recommendations vary for the amount of insulation necessary for peak energy savings, depending on factors such as climate conditions, the sections of your home being insulated and the kinds of materials used in your home's construction.

Insulation is rated by R-values
The R-value (or thermal resistance) of insulation is a measure of its ability to resist heat loss or heat gain. The higher the R-value, the better a material insulates.

An insulation's R-value is based on its performance in a 70°F environment with no air movement. Therefore, the rated R-value from the insulation's manufacturer may be much higher than its effective R-value if the insulation is not properly installed-or air leaks are not plugged before the insulation is added. Some types of insulation-such as blown-in wet cellulose, polyurethane and polyicynene-combine both air sealing and insulation in one step. The rated and effective R-values for these products are very similar, and they have a good performance record when installed correctly.

When you go shopping for insulation, it's important to remember that the product with the highest R-value per inch may not be the most cost-effective one. For example, when insulating a basement wall to an R-12 value, using 3 inches of an R-4 per inch insulation material might be less expensive than using 2 inches of an R-6 per inch product. To get the most insulating value for your money, compare the total costs of insulating an area to a specific R-value. In addition, keep in mind that some materials may settle after installation, reducing their effective R-value-so check the manufacturer's specifications before you buy.

Sidebar

The material in this article was adapted from Home Tightening, Insulation and Ventilation, a book published by the Iowa Energy Center. Besides offering more details on the topics discussed here, this publication describes energy-saving home improvement projects that may be eligible for rebates from local utility companies; low-income assistance and grant programs; special financing opportunities from banks, credit unions and other lending institutions; state incentives; and federal income tax credits.

To get a free copy of this book:

• Call your utility company to see if you can stop by the office and pick up a copy;
• Download a PDF copy at the Iowa Energy Center Web site: http://www.energy.iastate.edu/;
• Request a copy by e-mailing the Iowa Energy Center at iec@energy.iastate.edu; or
• Call the Iowa Energy Center at 515-294-8819 to ask for a copy to be sent to you by mail.

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Contact: Amy Myers, Iowa Energy Center, (515) 294-4391 myers@energy.iastate.edu

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